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    object对象 object里面key具有唯一性.
    <script>
        var obj={
            a:1,
            b:2,
            c:3,
            d:4,
            a:7
        }
        // 1.object.keys()方法:将对象的key值放到一个数组中返回
        console.log(Object.keys(obj));// ['a', 'b', 'c', 'd']

        // 2.object.values()方法:将对象的value值放到一个数组中返回
        console.log(Object.values(obj));//[7, 2, 3, 4]
    </script>
    
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